A device of this type is disclosed by EP-A-1 501 398. It consists essentially of a steam generator and a compressed air source, as well as of a steam supply line and a compressed air supply line connected to the latter and which is continued by the steam lance immersed in the milk. Therefore, the two media of steam and air are already mixed before the steam lance. Consequently, it is difficult to adapt the quality of the milk froth and to change it according to the type of drink to be prepared. Nowadays, devices of this type must satisfy high demands with regard to product quality although their conditions of use and operation often vary considerably from case to case.